Reducing magnet spacing (actual physical distance between a magnetic head read/write element and a magnetic layer of a magnetic disk) is useful for increasing recording density in magnetic storage device. Reducing the clearance (a gap distance between the very lowest point on the magnetic head and the upper surface of the magnetic disk) assists in achieving this reduction. Very precise contact detection is essential to achieve a clearance of anywhere from 1 nm or less. According to conventional methods, very precise contact detection and clearance control may be achieved using a heater element and a head-disk interface (HDI) contact sensor element positioned near a contact point on the magnetic head. However, the sensor is very sensitive in such methods, so minute interactions between the magnetic head and any lubricant applied to the upper surface of the magnetic disk or magnetic recording medium produces adverse effects, such as causing errors in determining contact between the head and the disk.
A perfluoropolyether (PFPE) derived from FOMBLIN Z (a brand name) produced by Solvay Solexis, for instance, is commonly used as a conventional disk lubricant, but the molecular weight of commercially available lubricants is distributed over a wide range and varies according to the lots of lubricant produced.
It has therefore been proposed to use only an extracted component having a molecular weight in a suitable range from this wider overall range, as disclosed in Japanese Patent Publication No. 12-315314A and U.S. Pat. No. 6,099,937. In Japanese Patent Publication No. 9-282642A and Japanese Patent Publication No. 18-228422A, it has been proposed to use a lubricant employing one or more types of perfluoropolyether (PFPE) having different terminal functional groups as a lubricant for improving bonding with the magnetic disk. Furthermore, in Japanese Patent Publication No. 18-70173A, a PFPE having an average of 1.0 to 5.0 hydroxyl groups in each molecule has been proposed as a lubricant to take account for planarity of the lubricant film and strong bonding force with the magnetic disk.
However, the abovementioned lubricant produces strong interactions between the lubricant and the magnetic head when contact between the head and the disk is determined, which means that contact is often erroneously detected and it is difficult to ensure very precise and stable contact determination. Furthermore, when a thickness of the lubricant film is reduced to a level which does not affect the contact determination, reliability is impaired due to other factors, such as corrosion resistance of the magnetic disk.
On the other hand, Japanese Patent Office (JPO) Publication No. 2008-16158A and JPO Publication No. 2002-192742A disclose technology in which a contact sensor element is fitted to a magnetic head, but these contact sensor have not been useful in providing an ideal combination, when the magnetic disk is taken into account, for effectively employing these contact sensors.
Accordingly, a thin film of lubricant is needed in order to reduce interactions between a magnetic head employing a contact sensor and a lubricant on the upper surface of a magnetic disk when any of the above described methods are used. Film-thinning referred to herein includes (1) simply reducing the thickness of the lubricant film; and (2) selecting a lubricant in which the lubricant molecules are capable of attaching/bonding at a low level to the surface of the magnetic disk in terms of the three-dimensional structure. As a result, interactions between the head and the disk may be restricted.
However, film thinning achieved by the methods described above involve risks in terms of reliability of the HDI, such as environment/contamination resistance and reduced lubricity (wear resistance).